Electrolytic capacitors are increasingly being used in the design of circuits due to their volumetric efficiency, reliability, and process compatibility. Electrolytic capacitors typically have a larger capacitance per unit volume than certain other types of capacitors, making them valuable in relatively high-current and low-frequency electrical circuits. One type of capacitor that has been developed is a wet electrolytic capacitor that includes an anode, a cathode current collector (e.g., aluminum can), and a liquid or “wet” electrolyte. Wet electrolytic capacitors tend to offer a good combination of high capacitance with low leakage current and a low dissipation factor. In certain situations, wet electrolytic capacitors may exhibit advantages over solid electrolytic capacitors. For example, wet electrolytic capacitors may operate at a higher working voltage than solid electrolytic capacitors. Additionally, wet electrolytic capacitors are often larger in size than solid electrolytic capacitors, leading to larger capacitance values.
In an effort to further improve the electrical performance of wet electrolytic capacitors, carbon powder has sometimes been applied to the cathode current collector. Unfortunately, it is difficult to directly bond carbon powder to certain types of current collectors. Thus, a variety of techniques have been developed in an attempt to overcome this problem. For example, U.S. Pat. No. 6,914,768 to Matsumoto, et al. describes the application of a carbonaceous layer to a cathode current collector. The layer containing a carbonaceous material (e.g., activated carbon), a conductive agent (e.g., carbon black), and a binder material (e.g., polytetrafluoroethylene, polyvinylidene fluoride, carboxymethylcellulose, fluoroolefin copolymer crosslinked polymer, polyvinyl alcohol, polyacrylic acid, polyimide, petroleum pitch, coal pitch, and phenol resins). Although the binder material may help adhere the carbonaceous material to the surface of the current collector, it is nevertheless believed to block the pores and surface of the carbonaceous material, thereby limiting its ability to increase the effective cathode surface area.
Thus, despite the benefits achieved with conventional wet electrolytic capacitors, a need currently for improvement nevertheless remains.